Repeated angiographies in male medical patients with peripheral arterial disease who did not undergo surgery disclosed radiological progression in 52% of 1,196 extremities followed up for one half to 8 years (2½) years on the average) Progression was more frequent in (1) extremities of patients 50 years of age and older than in those younger ones, (2) extremities of manifest diabetics, and (3) in superficial femoral arteries than in others. The most discriminating predictor of further progression, however, was the appearance of the initial angiogram, as evidenced by the following: Progression was (4) more frequent in arterial segments immediately proximal to occlusions than in those immediately distal, (5) more frequent in arteries or extremities with initial stenoses than in those without, and (6) was not primarily dependent on the presence or absence of occlusions.